That figure includes teachers in traditional public as well as in charter schools, K-12. Teachers who used their own money on classroom supplies spent an average of $479.

Teachers in districts that have higher poverty levels are more likely to be underfunded, according to the center. Resources are also lacking. It is precisely these two factors that motivate teachers to dig more deeply into their own pockets to help out.

Teachers do get a $250 tax deduction, but it's not a dollar-for-dollar reimbursement, says Meg Benner, senior consultant at the Center for American Progress. "It reduces taxable income," Benner said. "But a lot are spending double, if not more than the deduction itself."

The Center for American Progress has a proposal to boost wages for teachers. The reason is simple: Higher salaries will help attract and retain good teachers, according to the research and advocacy organization. Teacher pay is a significant factor in someone's decision to become a teacher, and to remain in the profession.

Teacher walkouts and strikes earlier this year show this is an issue that people care about. "The public is showing we need to invest more in our teachers to make sure kids have the quality teachers who can serve them well," Benner said.

"The public is showing we need to invest more in our teachers to make sure kids have the quality teachers who can serve them well."-Meg Benner, senior consultant, Center for American Progress

Schoolteachers' salaries lag behind those of other professionals with college degrees. "When we look at the gap, it's very significant," Benner said.

Instead of allowing this divide, the Center for American Progress has proposed using the federal tax code to create a tax credit for teachers.

It would be similar to the earned income tax credit, but would be used to substantially increase pay for public school teachers in high-poverty schools. Teachers could see an increase of more than $190 a week in take-home pay.

The proposal doesn't just give teachers the raise they deserve, considering their responsibilities, Benner says. Given the amount teachers spend out-of-pocket, it would also make up some portion of those costs.